21期say goodbye了，大家都跟上进度没有啊！？
怒吼一声：有！ O(∩_∩)O哈哈哈~~~
看回帖率有要爆棚的趋势 ~\(≧▽≦)/~ 22期大家都要继续加油，继续坚持！好不好？
怒吼三声：好！好！好！ 
夏天到了，是不是做小分队的时候被蚊子咬了？！分心有木有！
今天特地找的专题就是“蚊纸--mosquito”
最后还附上一篇简单实用的小文章---“简单有力的一招教你摆脱拖延症”
大家尽情享受吧~~~~~~~~~~~(>^ω^<)喵了个咪
Part I: Speed
Some Mosquitoes Become Immune to DEET After Just a Few Hours of Exposure
【Time 1】 If you’re someone that’s naturally irresistible to mosquitoes, a new finding published today in PLOS ONE could make for a rude awakening. A group of researchers from the London School of Hygiene and Tropical Medicine discovered that three hours after an exposure to DEET, many Aedes aegypti mosquitoes were immune to the chemical, ignoring its typically noxious smell and attempting to land on irresistible human skin.
Normally, DEET—short for N,N-Diethyl-meta-toluamide, which is the active ingredient in most insect repellents on the market—works because mosquitoes seem to find the chemical’s smell unpleasant and actively avoid landing on surfaces where it has been applied. But in this study, led by Nina Stanczyk, the researchers found mosquito behavior that runs contrary to scientists’ previous understanding of how the insects interact with the chemical.
DEET is used in the majority of insect repellents on the market. Image via Flickr user Spokenhope Initially, the researchers split a number of Aedes aegypti mosquitoes (a common species found on all continents, including North America) into two groups, each in a metal mesh cage. Then they had volunteers hold their arms about an inch over each cage, with one treated with a 20-percent DEET solution and another that had no repellent (a control arm).
Three hours later, they repeated the experiment, and counted exactly how many mosquitoes overcame the DEET and attempted to get through the metal mesh to reach the arms. They found that about half of the mosquitoes who’d been initially exposed to DEET on their first go-round seemed immune to the chemical during the second trial and tried to reach the DEET-covered arm, compared to the 10-20 percent that had attempted to do so during their first trial. This number was still less than the proportion of mosquitoes trying to reach the plain arm (70-80 percent). （words:303）
【Time 2】 Further proof the development of DEET immunity, though, lies in a third group of mosquitoes, who were exposed to a control arm first and a DEET arm second. Because they hadn’t had the chance to become habituated to the chemical, a much lower amount of them (less than 10 percent) tried to reach the DEET-covered arm.
To ensure that some sort of interaction between chemicals in human skin and DEET wasn’t responsible, the researchers also replicated the experiment with a heating device—to which mosquitoes are naturally attracted—that was also covered in DEET. The results were similar, indicating that the insects were somehow becoming habituated to DEET itself, regardless of the surface it was covering.
So why did the mosquitoes, as a whole, overcome their dislike of DEET? Previous studies by this group and others have found particular mosquitoes with a genetic mutation that made them innately immune to DEET, but they say that this case is different, because they didn’t demonstrate this ability from the start.
They suspect, instead, that the insects’ antennae became less chemically sensitive to DEET over time, as evidenced by electroantennography on the mosquitoes’ odor receptors after each of the tests—a phenomenon not unlike a person getting used to the smell of, say, the ocean or a manufacturing plant near his or her house.
Of course, this sort of aromatic habituation is significantly less convenient, because DEET-based repellents are relied upon not just to help us avoid irritating bites but also to stop the spread of mosquito-borne diseases like malaria and dengue. But the researchers don’t recommend dropping DEET entirely, for a few reasons.
For one, mosquitoes live as adults for only a few days at most, and the habituation likely isn’t passed along to offspring, so the odds that a particular mosquito you come across has already been exposed to DEET is pretty low. Additionally, even if it has, not all of the individual mosquitoes in the trial became used to the DEET, so it should still be somewhat effective as a repellent.
Most important, though, is the fact that we still haven’t developed any other repellent that is as consistently potent as DEET—so for now, they say, people living in areas with high risks of mosquito-borne illnesses have little other choice than to keep using it.
(Words:386)
http://blogs.smithsonianmag.com/science/2013/02/some-mosquitoes-become-immune-to-deet-after-just-a-few-hours-of-exposure/
Why Do Mosquitoes Bite Some People More Than Others?
【Time 3】
You come in from a summer hike covered with itchy red mosquito bites, only to have your friends innocently proclaim that they don’t have any. Or you wake up from a night of camping to find your ankles and wrists aflame with bites, while your tent mates are unscathed.
You’re not alone. An estimated 20 percent of people, it turns out, are especially delicious for mosquitoes, and get bit more often on a consistent basis. And while scientists don’t yet have a cure for the ailment, other than preventing bites with insect repellent (which, we’ve recently discovered, some mosquitoes can become immune to over time), they do have a number of ideas regarding why some of us are more prone to bites than others. Here are some of the factors that could play a role:
Blood Type Not surprisingly—since, after all, mosquitoes bite us to harvest proteins from our blood—research shows that they find certain blood types more appetizing than others. One study found that in a controlled setting, mosquitoes landed on people with Type O blood nearly twice as often as those with Type A. People with Type B blood fell somewhere in the middle of this itchy spectrum. Additionally, based on other genes, about 85 percent of people secrete a chemical signal through their skin that indicates which blood type they have, while 15 percent do not, and mosquitoes are also more attracted to secretors than nonsecretors regardless of which type they are. (words:247)
【Time 4】 Carbon Dioxide One of the key ways mosquitoes locate their targets is by smelling the carbon dioxide emitted in their breath—they use an organ called a maxillary palp to do this, and can detect carbon dioxide from as far as 164 feet away. As a result, people who simply exhale more of the gas over time—generally, larger people—have been shown to attract more mosquitoes than others. This is one of the reasons why children get bit less often than adults, on the whole.
Exercise and Metabolism In addition to carbon dioxide, mosquitoes find victims at closer range by smelling the lactic acid, uric acid, ammonia and other substances expelled via their sweat, and are also attracted to people with higher body temperatures. Because strenuous exercise increases the buildup of lactic acid and heat in your body, it likely makes you stand out to the insects. Meanwhile, genetic factors influence the amount of uric acid and other substances naturally emitted by each person, making some people more easily found by mosquitos than others.
Skin Bacteria Other research has suggested that the particular types and volume of bacteria that naturally live on human skin affect our attractiveness to mosquitoes. In a 2011 study, scientists found that having large amounts of a few types of bacteria made skin more appealing to mosquitoes. Surprisingly, though, having lots of bacteria but spread among a greater diversity of different species of bacteria seemed to make skin less attractive. This also might be why mosquitoes are especially prone to biting our ankles and feet—they naturally have more robust bacteria colonies.
Beer Just a single 12-ounce bottle of beer can make you more attractive to the insects, one study found. But even though researchers had suspected this was because drinking increases the amount of ethanol excreted in sweat, or because it increases body temperature, neither of these factors were found to correlate with mosquito landings, making their affinity for drinkers something of a mystery. (words:330)
【Time 5】 Pregnancy In several different studies, pregnant women have been found to attract roughly twice as many mosquito bites as others, likely a result of the fact the unfortunate confluence of two factors: They exhale about 21 percent more carbon dioxide and are on average about 1.26 degrees Fahrenheit warmer than others
Clothing Color This one might seem absurd, but mosquitoes use vision (along with scent) to locate humans, so wearing colors that stand out (black, dark blue or red) may make you easier to find, at least according to James Day, a medical entomologist at the University of Florida, in commentary he gave to NBC.
Genetics As a whole, underlying genetic factors are estimated to account for 85 percent of the variability between people in their attractiveness to mosquitoes—regardless of whether it’s expressed through blood type, metabolism, or other factors. Unfortunately, we don’t (yet) have a way of modifying these genes, but…
Natural Repellants Some researchers have started looking at the reasons why a minority of people seem to rarely attract mosquitoes in the hopes of creating the next generation of insect repellants. Using chromatography to isolate the particular chemicals these people emit, scientists at the UK’s Rothamsted Research lab have found that these natural repellers tend to excrete a handful of substancesthat mosquitoes don’t seem to find appealing. Eventually, incorporating these molecules into advanced bug spray could make it possible for even a Type O, exercising, pregnant woman in a black shirt to ward off mosquitoes for good. (words:250)
http://blogs.smithsonianmag.com/science/2013/07/why-do-mosquitoes-bite-some-people-more-than-others/#ixzz2Z2EVb7Xj
Finding Smells That Repel
【Time 6】
If you're one of those people whom mosquitoes tend to favor, maybe it's because you aren't sufficiently stressed-out. Insects have very keen powers of smell that direct them to their targets. But for researchers trying to figure out what attracts or repels the pests, sorting through the 300 to 400 distinct chemical odors that the human body produces has proved daunting.
Now scientists at Rothamsted Research in the U.K. have been making headway at understanding why some people can end up with dozens of bites after a backyard barbecue, while others remain unscathed. The researchers have identified a handful of the body's chemical odors—some of which may be related to stress—that are present in significantly larger concentrations in people that the bugs are happier to leave alone. If efforts to synthesize these particular chemicals are successful, the result could be an all-natural mosquito repellent that is more effective and safer than products currently available.
"Mosquitoes fly through an aerial soup of chemicals, but can home in on those that draw them to humans," says James Logan, a researcher at Rothamsted, one of the world's oldest agricultural-research institutions. But when the combination of human odors is wrong, he says, "the mosquito fails to recognize this signal as a potential blood meal."
The phenomenon that some people are more prone to mosquito bites than others is well documented. In the 1990s, chemist Ulrich Bernier, now at the U.S. Department of Agriculture's Agricultural Research Service, began looking for what he calls the "magic compounds" that attract mosquitoes. His research helped to show that mosquitoes are attracted to humans by blends of common chemicals such as carbon dioxide, released from the skin and by exhaling, and lactic acid, which is present on the skin, especially when we exercise. But none of the known attractant chemicals explained why mosquitoes preferred some people to others.
Rothamsted's Dr. Logan says the answer isn't to be found in attractant chemicals. He and colleagues observed that everyone produces chemicals that mosquitoes like, but those who are unattractive to mosquitoes produce more of certain chemicals that repel them.
Misguided Mosquitoes "The repellents were what made the difference," says Dr. Logan, who is interested in the study of how animals communicate using smell. These chemicals may cloud or mask the attractive chemicals, or may disable mosquitoes from being able to detect those attractive odors, he suggests. Besides delivering annoying bites, mosquitoes cause hundreds of millions of cases of disease each year. As many as 500 million cases of malaria are contracted globally each year, and more than one million people die from it, according to the Centers for Disease Control and Prevention. Mosquitoes can also spread West Nile virus, dengue fever, yellow fever and other illnesses.
Currently the most effective repellents on the market often contain a chemical known as DEET, which has been associated in some studies with potential safety concerns, such as cancer and Gulf War syndrome. It also damages materials made of plastic. The federal Environmental Protection Agency has determined that DEET, when used as directed, is safe.
The Rothamsted team set out to get the mosquitoes' viewpoint. The researchers separated human volunteers into two groups—those who were attractive to mosquitoes and those who weren't. They then put each of the volunteers into body-size foil bags for two hours to collect their body odors. Using a machine known as a chromatograph, the scientists were able to separate the chemicals. They then tested each of them to see how the mosquitoes responded. By attaching microelectrodes to the insects' antennae, the researchers could measure the electrical impulses that are generated when mosquitoes recognize a chemical.
Dr. Logan and his team have found only a small number of body chemicals—seven or eight—that were present in significantly different quantities between those people who were attractive to mosquitoes and those who weren't. They then put their findings to the test. For this they used a so-called Y-tube olfactometer that allows mosquitoes to make a choice and fly toward or away from an individual's hand. After applying the chemicals thought to be repellant on the hands of individuals known to be attractive, Dr. Logan found that the bugs either flew in the opposite direction or weren't motivated by the person's smell to fly at all.
The chemicals were then tested to determine their impact on actual biting behavior. Volunteers put their arms in a box containing mosquitoes, one arm coated with repellent chemicals and the other without, to see if the arm without the coating got bitten more.
Significant Repellency The group's latest paper, published in March in the Journal of Medical Entomology, identified two compounds with "significant repellency." One of the compounds, 6-methyl-5-hepten-2-one, is a skin-derived compound that has the odor of toned-down nail-polish remover, according to George Preti, an organic chemist at the Monell Chemical Senses Center in Philadelphia, who is involved in a separate line of research into insect-biting behavior. The other, identified in the paper as geranylacetone, has a pleasant odor, though there is some question about whether the chemical is formed by the human biochemical process or is picked up in the environment, Dr. Preti says.
Dr. Logan declined to comment about the specific chemicals because of proprietary concerns. He says the findings have been patented and the group is working with a commercial company to develop the compounds into a usable insect repellent. One issue that still needs to be resolved: how to develop a formulation of the repellent chemicals that will stay on the skin, rather than quickly evaporating as they do naturally. The hope is to get a product to market within a year or two, he says.
Some of the chemicals researchers identified are believed to be related to stress, Dr. Logan says. Previous research has shown that these particular chemicals could be converted from certain other molecules and this could be as a result of oxidation in the body at times of stress, he says. However, it's not clear if the chemicals observed by the Rothamsted researchers were created in this way, and research is continuing to answer this and other questions.
Dr. Logan suggests that mosquitoes may deem hosts that emit more of these chemicals to be diseased or injured and "not a good quality blood meal." Proteins in the blood are necessary for female mosquitoes to produce fertile eggs, and Dr. Logan says it might be evolutionarily advantageous for mosquitoes to detect and avoid such people.
Other Research
Other research includes an effort by scientists at the University of California, Riverside, who published a paper in the journal Nature last week identifying a recently discovered class of molecules that inhibit fruit flies' and mosquitoes' ability to detect carbon dioxide. Mosquitoes can detect carbon dioxide emissions from long ranges, so turning off the ability to detect the gas, perhaps by releasing the inhibiting molecules into the environment, may be a way of keeping the bugs at bay, the researchers suggest. Another team, at the Monell Chemical Senses Center, is launching a study into whether the taste of human skin and blood are related to the insects' interest in biting certain individuals. (words:1193)
http://online.wsj.com/article/SB10001424052970204660604574378933761528214.html
One Powerful Tip to Stop Procrastination in its Tracks
【Time 7】
Isn’t it amazing how energetically we clean our closets or organize the movie collection when a dreaded project is looming? Especially when that project feels abstract and difficult…I battle with this type of procrastination a LOT. And after much trial and error, I’ve found a simple system that works for me.
If, like me, you tend to put things off or can’t seem to stick with it once you start, then I am confident it will help you too. Here it is:There are two critical parts to procrastination. One is difficulty getting started on something you need to do. The other is not sticking to something you started (and getting distracted by more exciting or easier things).
Today, I’m going to tell you how to beat the second one. So let’s say you have just started a new diet, or an important work project. Most people are able to see it as a series of small steps that have to be done one day at a time to get to the successful end point.But if you are a chronic procrastinator, you will have trouble seeing the process, and instead you see only the final product (the super thin, six pack physique; or the perfectly done work project that impresses your boss and his boss). This is a big problem, kind of like seeing the forest and forgetting the trees. What happens when you can only imagine the perfect final product?
You are unable to imagine the steps it would take to get there and thus feel anxious and overwhelmed. It’s like being told to get to the moon and all you have for help is a mental picture of you standing on the moon.Who wouldn’t get anxious?! So to get rid of the anxiety, you convince yourself that ‘there’s still plenty of time” and that you will “get it done perfectly tomorrow” and turn to Facebook or cleaning out your closets. This inability to imagine the process is one of the biggest problems faced by those of us who struggle with procrastination.
So what’s the solution? Simple: 1. Write down the smaller tasks under each project and select the first small task. 2. Then, make a pre-decision about what you will do when you feel frustrated or a distraction beckons. A pre-decision has the “If X, then Y formula”.
For example, “If I feel anxious or frustrated, then I will remind myself to just focus on this one small piece and not the entire forest” OR “If I begin to doodle or think of calling my friend, then I will call my friend and ask him to help me stay on track” etc;
Only you know what your usual distractions are and so you can make “If X, then Y” pre-decisions that are uniquelydesigned for you.
I used this technique to lose 20 pounds in the last few months. My main problem is resisting a temptation to eat desserts. I allow myself to eat one yummy dessert a week. When my mind asks for it any other time, I have a pre-decision that goes like this “If my mind makes me crave a dessert during the week, I will imagine that dessert morphing into a pound of fat in front of my eyes”.Trust me, it worked.
The trick here is to have made this pre-decision ahead of time (writing it down is even better) so that you can do it automatically without having to thinkwhen you are hit by distraction or temptation.
Every decision point in your life is like a road diverging in the woods. By learning to imagine the process and having a plan to deal with obstacles, you can beat procrastination and choose the road that unleashes your full potential.
（words：626）
http://xue.youdao.com/biarticle.a?articleId=9210527079893287395&date=2013-07-04&position=read-history&channelType=public | 
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发表于 2013-7-15 21:16:42
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